1. Field of the Invention
The present invention relates to an internal combustion engine system comprising a reformer provided with a reforming catalyst for recirculating a part of the exhaust gas to an exhaust circulation path communicating with an intake path and an exhaust path communicating with the combustion chamber of an internal combustion engine, and generating a hydrogen-containing gas using a reforming fuel supplied into the exhaust gas.
2. Background Information
Conventionally, there have been known exhaust circulation systems for recirculating and mixing a part of the exhaust gas discharged from an internal combustion engine into the intake system, and thereby lowering the maximum temperature during combustion and reducing the amount of NOx in the exhaust gas.
There have been proposed, as an application of the exhaust circulation system, internal combustion engine exhaust gas recirculation (EGR) reforming systems for supplying a fuel to the recirculated exhaust gas, performing a reforming reaction (endothermic reaction) on a reforming catalyst using the heat of the exhaust gas, and recirculating a gas containing hydrogen and carbon monoxide into the intake system, whereby the exhaust heat is recovered and fuel economy is improved (e.g., Japanese Laid-Open Patent Publication No. 61-35375).
There have also been proposed internal combustion engine EGR reforming systems in which degradation of the reforming catalyst is detected, whereby a deterioration in fuel economy and fluctuations in the torque are prevented (e.g., Japanese Patent No. 4013704). Possible reforming reactions include a water vapor reforming reaction in which water vapor in the exhaust gas is used, and dry reforming in which carbon dioxide is used; however, both reactions are prone to carbon deposition.
While the reforming reaction is performed by supplying fuel into the exhaust gas, depending on the fuel supply method, there is a possibility of the fuel not mixing with the exhaust gas component in a uniform manner and of a localized region having a low S/C or CO2/C ratio being generated. Under a condition of low S/C or CO2/C ratio, carbon deposition is more likely.
When carbon deposition occurs, the reforming catalyst eventually ceases to function, and it no longer becomes possible to obtain the desired hydrogen-containing gas. There are instances in which the performance of the reforming catalyst, having been reduced by carbon deposition, is restored through burn-off by an oxidation reaction using an oxygen-containing gas. However, since the combustion temperature increases in correspondence with the amount of carbon deposition, the temperature will rapidly increase if a large amount of carbon has been deposited. A rapid increase in temperature may lead to thermal degradation of the catalyst. The principal thermal degradation in such an instance is sintering of the catalyst particles, and much of the thermal degradation is permanent degradation from which regeneration is difficult.
In addition, with regards to the performance decrease, degradation, and abnormalities in the reforming catalyst, a variety of detection methods such as using the reforming catalyst temperature, hydrogen concentration, and carbon monoxide concentration have been proposed. On the reforming catalyst, a hydrogen-containing gas continues to be generated while carbon deposition is in progress.